Exposure control device and exposure control method

1. An exposure control device comprising: an illumination level determination unit configured to determine that an illumination level of an external light illuminance corresponds to one of a plurality of illuminance levels; a plurality of timers each provided for a corresponding one of a plurality of change modes, the change modes being defined among the plurality of illuminance levels, or among a plurality of exposure levels for an exposure of a vehicular camera; a timer operating unit configured to operate each of the plurality of timers in accordance with a state of change of the illuminance level of the external light illuminance; and an exposure level determination unit configured to determine one of the exposure levels for the exposure of the vehicular camera based on a count state of each of the plurality of timers.

2. The exposure control device according to claim 1 , wherein the plurality of timers include a first timer, a second timer, and a third timer; the plurality of illuminance levels include a first illuminance level, a second illuminance level, and a third illuminance level; the exposure levels include a first exposure level, a second exposure level, and a third exposure level; and the timer operating unit is configured to count up the first timer and resets the second timer when the illuminance level of the external light illuminance changes from the first illuminance level to the second illuminance level between the first illuminance level and the third illuminance level, count up the second timer and resets the first timer when the illuminance level of the external light illuminance changes from the second illuminance level to the first illuminance level, and count up the first timer and the third timer and resets the second timer when the illuminance level of the external light illuminance changes from the first illuminance level to the third illuminance level; and the exposure level determination unit is configured to change the exposure for the exposure of the vehicular camera to the second exposure level between the first exposure level and the third exposure level when the first timer has been counted up, change the exposure for the exposure of the vehicular camera to the first exposure level when the second timer has been counted up, and change the exposure for the exposure of the vehicular camera to the third exposure level when the third timer has been counted up.

3. The exposure control device according to claim 2 , wherein the exposure level determination unit changes the exposure of the vehicular camera to the third exposure level when both the first timer and the third timer have been counted up.

4. The exposure control device according to claim 2 , wherein the plurality of timers further include a fourth timer and a fifth timer; and the timer operating unit is configured to count up the fourth timer and resets the fifth timer when the illuminance level of the external light illuminance changes from the second illuminance level to the third illuminance level, and count up the fifth timer and resets the fourth timer when the illuminance level of the external light illuminance changes from the third illuminance level to the second illuminance level; and the exposure level determination unit is configured to change the exposure of the vehicular camera to the third exposure level when the fourth timer has been counted up, and change the exposure of the vehicular camera to the second exposure level when the fifth timer has been counted up.

5. The exposure control device according to claim 4 , wherein the plurality of timers further include a sixth timer; and the timer operating unit counts up the sixth timer and resets the third timer when the illuminance level of the external light illuminance changes from the third illuminance level to the first illuminance level, and the exposure level determination unit changes the exposure of the vehicular camera to the first exposure level when the sixth timer has been counted up.

6. The exposure control device according to claim 5 , wherein the timer operating unit is configured to count up the first timer and resets the second timer and the sixth timer when the illuminance level of the external light illuminance changes from the first illuminance level to the second illuminance level, count up the fourth timer and resets the fifth timer when the illuminance level of the external light illuminance changes from the second illuminance level to the third illuminance level, count up the first timer and the third timer, and resets the second timer, the fifth timer, and the sixth timer, when the illuminance level of the external light illuminance changes from the first illuminance level to the third illuminance level, count up the fifth timer and resets the third timer and the fourth timer when the illuminance level of the external light illuminance changes from the third illuminance level to the second illuminance level, count up the second timer and resets the first timer when the illuminance level of the external light illuminance changes from the second illuminance level to the first illuminance level, and count up the fifth timer and the sixth timer, and resets the first timer, the third timer, and the fourth timer, when the illuminance level of the external light illuminance changes from the third illuminance level to the first illuminance level.

7. The exposure control device according to claim 5 , wherein the exposure level determination unit changes the exposure of the vehicular camera to the first exposure level when both the fifth timer and the sixth timer have been counted up.

8. The exposure control device according to claim 4 , wherein the exposure level determination unit changes the exposure of the vehicular camera to the third exposure level when both the first timer and the fourth timer have been counted up.

9. The exposure control device according to claim 4 , wherein the exposure level determination unit changes the exposure of the vehicular camera to the first exposure level when both the second timer and the fifth timer have been counted up.

10. The exposure control device according to claim 1 , wherein the illumination level determination unit is configured to: determine whether the illumination level of the external light illuminance has decreased using a first luminance-level determination threshold; and determine whether the illumination level of the external light illuminance has increased using a second determination threshold, the second luminance-level determination threshold, the second luminance-level determination threshold being set to be higher than the first luminance-level determination threshold.

11. An exposure control method of a vehicle-mounted camera, comprising: determining that an illumination level of an external light illuminance corresponds to one of a plurality of illuminance levels; operating each of a plurality of timers, each provided for a corresponding one of a plurality of change modes, the change modes being defined among the plurality of illuminance levels, or among a plurality of exposure levels for an exposure of a vehicular camera; and determining one of the exposure levels for the exposure of the vehicular camera based on a count state of each of the plurality of timers.

12. The exposure control method according to claim 11 , wherein the plurality of timers include a first timer, a second timer, and a third timer; the plurality of illuminance levels include a first illuminance level, a second illuminance level, and a third illuminance level; the exposure levels include a first exposure level, a second exposure level, and a third exposure level; and operating of the plurality of timers includes: counting up the first timer and resetting the second timer when the illuminance level of the external light illuminance changes from the first illuminance level to the second illuminance level between the first illuminance level and the third illuminance level, counting up the second timer and resetting the first timer when the illuminance level of the external light illuminance changes from the second illuminance level to the first illuminance level, and counting up the first timer and the third timer and resetting the second timer when the illuminance level of the external light illuminance changes from the first illuminance level to the third illuminance level; and determining the one of the exposure levels includes: changing the exposure for the exposure of the vehicular camera to the second exposure level between the first exposure level and the third exposure level when the first timer has been counted up, changing the exposure for the exposure of the vehicular camera to the first exposure level when the second timer has been counted up, and changing the exposure for the exposure of the vehicular camera to the third exposure level when the third timer has been counted up.

13. The exposure control method according to claim 12 , wherein, determining the one of the exposure levels includes changing the exposure of the vehicular camera to the third exposure level when both the first timer and the third timer have been counted up.

14. The exposure control method according to claim 12 , wherein the plurality of timers further include a fourth timer and a fifth timer; and operating of the plurality of timers includes: counting up the fourth timer and resetting the fifth timer when the illuminance level of the external light illuminance changes from the second illuminance level to the third illuminance level, and counting up the fifth timer and resetting the fourth timer when the illuminance level of the external light illuminance changes from the third illuminance level to the second illuminance level, and determining of the one of the exposure levels includes: changing the exposure of the vehicular camera to the third exposure level when the fourth timer has been counted up, and changing the exposure of the vehicular camera to the second exposure level when the fifth timer has been counted up.

15. The exposure control method according to claim 14 , wherein, the plurality of timers further include a sixth timer; and operating of the plurality of timers includes counting up the sixth timer and resetting the third timer when the illuminance level of the external light illuminance changes from the third illuminance level to the first illuminance level, and determining of the one of the exposure levels includes changing the exposure of the vehicular camera to the first exposure level when the sixth timer has been counted up.

16. The exposure control method according to claim 15 , wherein, operating of the plurality of timers includes: counting up the first timer and resetting the second timer and the sixth timer when the illuminance level of the external light illuminance changes from the first illuminance level to the second illuminance level, counting up the fourth timer and resetting the fifth timer when the illuminance level of the external light illuminance changes from the second illuminance level to the third illuminance level, counting up the first timer and the third timer and resetting the second timer, the fifth timer, and the sixth timer, when the illuminance level of the external light illuminance changes from the first illuminance level to the third illuminance level, counting up the fifth timer and resetting the third timer and the fourth timer when the illuminance level of the external light illuminance changes from the third illuminance level to the second illuminance level, counting up the second timer and resetting the first timer when the illuminance level of the external light illuminance changes from the second illuminance level to the first illuminance level, and counting up the fifth timer and the sixth timer and resetting the first timer, the third timer, and the fourth timer, when the illuminance level of the external light illuminance changes from the third illuminance level to the first illuminance level.

17. The exposure control method according to claim 15 , wherein, determining of the one of the exposure levels includes changing the exposure of the vehicular camera to the first exposure level when both the fifth timer and the sixth timer have been counted up.

18. The exposure control method according to claim 14 , wherein, determining of the one of the exposure levels includes changing the exposure of the vehicular camera to the third exposure level when both the first timer and the fourth timer have been counted up.

19. The exposure control method according to claim 14 , wherein, determining of the one of the exposure levels includes changing the exposure of the vehicular camera to the first exposure level when both the second timer and the fifth timer have been counted up.

20. The exposure control method according to claim 11 , wherein, further comprising: determining whether the illumination level of the external light illuminance has decreased using a first luminance-level determination threshold; and determining whether the illumination level of the external light illuminance has increased using a second luminance-level determination threshold, the second luminance-level determination threshold being set to be higher than the first luminance-level determination threshold.